The present invention relates to a cutting tool for chip forming machining preferably for milling, comprising a holder and a cutting insert, said cutting insert having a generally circular basic shape and including at least one cutting edge created by the transition between an upper face and an edge face of the cutting insert, said upper face being a rake face and said edge face being a clearance face, said holder and cutting insert having first means for preventing rotation of the insert about a center axis. The invention further relates to a cutting insert and a method for preventing rotation of a cutting insert.
In tools for metal cutting having indexable cutting inserts of hard and wear resistant material the cutting edges are subjected to wear and sometimes some part of or the entire cutting edge collapses. If a small insert fractures, only the cutting edge collapses without any risk for damage to the tool body. If a large insert fractures, the risk of damage to the tool body increases to an essential degree. If the cutting insert has no shim, an insert fracture often gives rise to damages of the tool body. In order to avoid such damages it is usual that the cutting insert rests on a shim of cemented carbide. A usual combination is a cutting insert having a thickness of about 5 mm and a shim having a thickness of 3-5 mm. This results in a total thickness of the cutting insert and the shim of 8-10 mm.
Riviere U.S. Pat. No. 5,147,158 discloses a polygonal cutting insert having an integrated shim so as to provide a fracture zone.
Rescigno U.S. Pat. No. 5,346,336 shows a circular metal cutting insert provided with five equidistant flat facets on the clearance surface. The facets are provided to constitute defined positions when indexing the cutting insert. Each facet forms an acute angle relative to the central axis of the cutting insert. A retention screw secures the insert to the insert seat of a holder. In the known tool, friction is not a major contributor against unwanted rotation of the insert. The locating surfaces of the insert will be worn such that the position of the insert in the seat will be increasingly less accurate during use. Furthermore the known insert lacks fracture zones so as to prevent an insert breakage from transferring into the seat or shim.